pgsql: pg_get_partkeydef: return NULL for non-partitions

pg_get_partkeydef: return NULL for non-partitions

Our general rule for pg_get_X(oid) functions is to simply return NULL
when passed an invalid or inappropriate OID. Teach pg_get_partkeydef to
do this also, making it easier for users to use this function when
querying against tables with both partitions and non-partitions (such as
pg_class).

As a concrete example, this makes pg_dump's life a little easier.

Author: Amit Langote

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/0c76c2463e8ab4cfd633ad8de259050e3f28b78f

Modified Files
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src/backend/utils/adt/ruleutils.c | 20 ++++++++++++++------
src/test/regress/expected/rules.out | 6 ++++++
src/test/regress/sql/rules.sql | 1 +
3 files changed, 21 insertions(+), 6 deletions(-)